The present disclosure relates to a zoom lens and an imaging apparatus, particularly, a zoom lens, which optically corrects image blur caused by hand shake and the like at the time of photography, and an imaging apparatus having the zoom lens.
Hand shake, which occurs at the time of photography, and vibration, which is transferred to a photographing system at the time of photographing in a moving object such as a vehicle, causes blurring in a photographed image. In particular, in an optical system of which the zoom ratio is large, the angle of view decreases in the telephoto end state, even minute hand shake causes large image blur. In order to correct such image blur, there have been hand shake correction optical systems that correct image blur by shifting a partial lens group constituting a lens system in a direction substantially perpendicular to the optical axis so as to shift image position and correct fluctuation in aberrations caused when the image position is shifted.
In the hand shake correction optical system, on the basis of a shake correction coefficient, shift of an image caused by hand shake and the like is corrected. Assuming that the focal length of the whole lens system is f and the angle of hand shake is θ, an amount of image shift yb caused by the hand shake is calculated by the following expression.yb=f·tan θ
Assuming that the shake correction coefficient of the shifted lens group is B, an amount of lens shift SL, which is necessary to correct the image shift amount yb, can be obtained by the following expression.SL=−f·tan θ/B 
Hence, as the shake correction coefficient B is larger, it is possible to correct hand shake with a smaller amount of lens shift SL.
The hand shake correction optical system is able to function as an optical hand shake correction system by combining, for example, a detection system, a control system, and a driving system. Here, the detection system detects the shaking of the camera caused by hand shake. The control system applies an amount of correction to a lens position on the basis of the signal which is output from the detection system. The driving system shifts a prescribed lens on the basis of the output from the control system.
In the driving system of the hand shake correction optical system, there have been proposed driving systems that correct image blur by shifting a part of the third lens group or the whole third lens group (for example, refer to FIG. 1 of each of Japanese Unexamined Patent Application Publication Nos. 7-128619 and 7-199124). However, the third lens group is positioned in the vicinity of the aperture diaphragm, and the rays pass therethrough in a state where the diameter of rays is large. Hence, fluctuation in aberrations, which are caused by the shift of the shift lens group, such as coma aberration increases, and thus a correctable angle of hand shake is limited to about 0.5°. Further, a problem arises in that a driving mechanism, which shifts the shift lens group, tends to interfere with a mechanism, which drives the aperture diaphragm, or tends to interfere with a mechanism which drives a lens group such as the second lens group or the fourth lens group which is movable in the direction of the optical axis.
In this respect, there have been proposed techniques of shifting a part or the whole of the final lens group which is positioned to be closest to the image side (for example, refer to FIG. 1, FIG. 1, and FIG. 2 of Japanese Unexamined Patent Application Publication Nos. 2006-276475, 2006-330341, and 2008-134334, respectively). In this case, in the final lens group, the rays pass therethrough in a state where the diameter of rays is small. Hence, the shift lens group has many advantages such as a decrease in sensitivity to the eccentricity of the shift lens group.